N-type polycrystalline higher manganese silicide ( MnSi 1.7) films are prepared on thermally oxidized silicon substrates by magnetron sputtering. MnSi 1.85, Si , and carbon targets are used in the experiments. By co-sputtering of the MnSi 1.85 and Si targets, n-type MnSi 1.7 films are directly obtained. By increasing the Si content to the deposited films, both the Seebeck coefficient and electrical resistivity increase to high values. A Si intermediate layer between the MnSi 1.7 film and substrate plays an important role on the electrical properties of the films. Without the interlayer, the Seebeck coefficient is not stable and the electrical resistivity is higher. For preparation of MnSi 1.7 films by solid phase reaction, a sandwich structure Si / MnSi x/ Si (x < 1.7) and thermal annealing are used. A carbon cap layer is used as a doping source. With the carbon doping, the electrical resistivity of the MnSi 1.7 film decreases, while the Seebeck coefficient increases slightly. For reactive deposition, the MnSi x (x < 1.7) film is directly deposited on the heated substrate with a Si intermediate layer. By using a Si cap layer, a MnSi 1.7 film with a Seebeck coefficient of -292 μ V/K and electrical resistivity of 23 × 10-3 Ω- cm at room temperature is obtained. The power factor reaches 1636 μW/mK2 at 483 K. With such a high power factor, the n-type MnSi 1.7 material may be superior to p-type MnSi 1.7 material for the development of thermoelectric generators. Several smaller (0.036 - 0.099 eV ) and intermediate (0.10 - 0.28 eV ) activation energies are observed from the curves of logarithm of the resistivity versus reciprocal temperature. The larger activation energies (0.35 - 1.1 eV ) are consistent with the reported energy band gaps for higher manganese silicides.
The effect of base pressure and manganese oxidation on preparation of Mn3O4 and higher manganese silicide
